The chrome button on my cars handbrake was well worn with all the chrome flaking off and looked pretty naff, I decided I'd have a go at replacing it, after not finding much info on the net I opted to buy a complete handbrake off ebay and have a go at it, in the end it turned out very easy...
1) Buy a donor handbrake from a forum trader, breakers or ebay etc, the button is available new but comes complete with release rod/spring as shown here:
http://www.ecstuning.com/Volkswagen-Jetta_IV_GLI--1.8T/Interior/Parking_Brake/ES257302/ so its up to you which you decide cheaper/easier.
2) Pull off leather handbrake handle, I did it by moving it to full height, place bracket part under feet and grab leather handle and pull hard.. it unclipped and pulled straight off no probs. (You can remove one fitted in car too.. you need to be pretty strong though)
3) Remove the chrome button by hand, now the leather handle part is off its easy to get button off, just pull from rear and it unclips and slides off. (If you opt to buy it new I am not sure the button will remove from the rod part the same, we can assume it would but as I didn't go down that route I can't confirm it to be the same as doing it my way with a used one)
4) Next remove the worn button on your cars handbrake... use a pair of pliars or similar, I use some electrical wire strippers I had to hand, trick is to pull it by gripping it not crushing it.
5) Now take the new button and push it on till it clicks into place. (make sure if you're parked on a slope that you place foot on brake pedal just in case car moves)
Hope that helps
